Process for froth flotation dressing



United States Patent Office Patented Nov. 6, 1956 PROCESS FOR FROTHFLOTATION DRESSING Wilhelm Reerink, Essen-Bredeney, Walter Miischenborn,Essen, and Erich Niitzold, Essen-Haarzkopf, Germany No Drawing.Application October 30, 1952, Serial No. 317,824

8 Claims. (Cl. 209-49) The invention concerns a process for the frothflotation dressing of material containing various components of varyingwettability, and espeically of complex ores, coal slimes and othercoal-containing products.

The purpose of the invention is the improvement and simplification ofthe known flotation process, especially in the sense of a reduction inthe quantities of flotationreagents required and also of a reduction inthe size of the equipment.

In the known froth flotation process, the minerals or the like which areto be separated are mixed with water, each litre containing usuallybetween 100 and 300 grammes of solid material and forming the so-calledflotation pulp. This is added to the flotation cells and to 'it areadded fixed quantities of flotation reagents of various types, such ascollecting, frothing and regulating agents.

By means of strong agitation by agiting mechanisms or by air the pulp iswell stirred and at the same .time aerated, i. e. very fine air bubblesare produced by the stirring or blowing.

The separation results from the fact that the flotation reagents combinewith the various components of the material, such as ores or minerals,and affect differentially the reaction to air and water of the surfacesof the particles, so that it is possible to lift definite fractions inthe froth to the surface of the pulp and to remove them, eithertogether, singly or in succession. For this purpose the quantities offlotation reagents used in relation to the amounts of pulp arerelatively small, for example, given often an addition of only 200-300grammes of flotation reagents for every to 10 cubic metres of pulp. inconsequence, the effect of the reagent is very limited, as in such aquantity of pulp it can only impinge more or less by chance on the ores,minerals or the like to be collected. Its effect is further weakened byother circumstances caused by the properties of the pulp.

The obvious possibility of overcoming these disadvantages by increasingthe concentration of flotation reagents would mean in general aneconomically unfavourable increase in the amount of these used. Afurther disadvantage of the known processes is that in producing therequired degree of separation, a very large number of flotation cells isnecessary in order to rework the pulp continuously, which leads toexpensive installations of comparatively large size.

The invention provides a froth flotation process which, withcomparatively low expenditure of flotation reagents and furthermore asmaller number of flotation cells, or even in certain conditions acomplete absence of these cells, permits the attainment of equal or incertain circumstances even more favourable results.

The basis of the process is that the raw material for flotation and theflotation reagents are brought together in such manner that a forcedaction between the reagents and the raw material is caused. It consistsin that after the flotation reagents are added to the material forflotation the mixture of raw material and agents is subjected to aforcing treatment in which it is at presures other than atmospheric, andthe material which has been so treated or the pulp produced therefrom isthen separated by aeration on the froth flotation principle. For thispurpose pneumatic flotation cells are preferably used.

It is especially advantageous if the mixture to be separated is veryfinely ground and is subjected to the forced treatment in a condition inwhich it is capable of flowing, i. e. in the form of thicker or thinnerpulp, and in this state is either subjected to static presuredifferences in containers, preferably with simultaneous agitating andshaking motion, or more advantageously is forced through narrowcross-sections, for example slits, nozzles or the like. In the case ofmaterial containing little water, being for example in a crumbly orpasty condition, the foreing treatment may consist of a thoroughkneading in a kneading machine, mixing pump, kneading pump or the like.In such cases the requisite amount of water must be added to the mixtureat a later stage, either in the agitator or in the flotation cellsthemselves.

The pressure arising in this treatment, which in certain cases can be anegative pressure, causes with certainty a combination between therequired minerals or the like to be collected and the flotationreagents, and a detachment of the layer of water from the surfaces.

As an alternative to the above method the forcing treatment may beachieved by causing the mixture in pulp form to impinge onbaffle-plates. This method can also be combined with the forcing of thepulp through narrow cross-sections as a final step to further improvingthe effect of the first treatment.

It may be found advantageous if the flotation reagent and/ or the pulpare heated before the forcing treatment.

Material treated in the manner described need only be erated in theusual way to achieve a separation into concentrate rising with thefroth, and waste or gangue.

The forcing treatment will usually take place before introdution of thematerial into the flotation cells. It is however possible to combine thetwo directly, by forcing the pulp intothe cells through narrowcross-sections. This may take place for example in an axial directionthrough the agitator, and for this purpose an apparatus working on theprinciple of a baffle-plate mill may for example be placed under theagitator.

In a special embodiment of the new process, the mixture of raw materialand flotation reagents, when submitted to the forcing treatment, inaddition to the reagents already present contains air or gaseousmaterial or else gaseous material which itself will act as a reagent,the air or gas being added in very finely divided form.

By this method a froth containing the concentrate will already have beenproduced before the forcing treatment, so that in some cases it will bepossible to omit any further separation treatment, and only be necessaryto lead the pulp, after forcing treatment with simulltaneous aeration,into receiving vessels; the concentrate can then be removed directlyfrom the surface of the pulp by suitable scraping-off means, such as forexample froth-scrapers, froth bucket-conveyors, discharge bands and thelike.

For carrying out the aeration process during the course of the forcingtreatment, the latter is advantageously performed, especially with themore watery mixtures, by socalled Pallmann baffle-plate mills orsimilarly working pumps or apparatus with pressure nozzles. Baflie platemills are well known as disin-tegrators, and generally provide aconfined zone between a rotating and a stationary plate in which isdisposed a counter-rotating impeller, the feed being axial and thedischarge being through constrictions, such as slits or apertures,between the peripheries of the plates. The material is subjected tointensive turbulence in the confined zone and is then forced through theperipheral apertures, which provides shearing and frictional forces dueto the developed pressure, and the sudden release thereof.

With the use of such machines a suitable flotation froth is createdimmediately, and the concentrates rise directly into the froth as soonas the pulp leaves the machine.

It has been demonstrated, for example, that with this method, using onlya small quantity of flotation reagents, coal which could otherwisescarcely be floated, passes immediately into the froth concentrate andwith only one or two repetitions of the operations pure waste materialis discharged.

In certain circumstances a single pressure treatment in a baffle-platemill of the type mentioned will sufiice to separate all the coal or thelike as a froth concentrate, so that it is only necessary to transferthe treated material into a settling tank and remove the rising frothconcentrate.

A further special advantage of this procedure is that with thebaffle-plate mill disintegration of the material takes placesimultaneously with the forcing treatment.

It may be preferable to allow the treated pulp to impinge on a liquidsurface. In certain cases this enables flotation cells to be completelydispensed with, or to be used only for the subsequent collection of anyvaluable components remaining in the pulp.

In addition to those already described, the new process has a furtheradvantage of fundamental importance based on the complete wettingachieved.

It is furthermore possible to replace the comparatively expensiveflotation reagents used in the known flotation processes by using forthis purpose less expensive and much more easily obtainable bituminousmaterials, such as high boiling point hydrocarbons of high pour point,for example fuel oils and even tar, pitch, distillation residue and thelike, all materials which do not normally form flotation froth.

When, in accordance with one of its special features, the new process iscarried out at a suitably raised temperature, bituminous materials canbe used which at normal temperatures are not liquid.

The use of said low-grade materials as flotation agents also enables thenew process to proceed by mere aeration of the pulp, which may followthe forcing treatment, or may with special advantage be performedsimultaneously with it, to achieve an ideal flotation effect andexcellent separation. When aeration is performed in the same machine asthe pre-treatment, for example in a baflle-plate mill of the knownPallmann Mill construction, the pulp need only be transferred to asuitable apparatus, such as a flotation machine, agitator or even asettling tank and the concentrate removed therefrom. If required,additional aeration can be carried out in these apparatus, oralternatively the entire aeration process may be performed therein.

The possibility of using low-grade oils and the like as flotationreagents instead of expensive special oils and reagents in this newprocess, with an oil-film completely covering the particles to be raisedinto the concentrate makes the flotation principle applicable to coarsermaterial, the pure components of which would not rise into theconcentrate under the influence of known flotation agents. It has beenfound that even such particles of material when treated in accordancewith the invention will readily float to the surface. The consequentincrease in the applicability of the froth flotation process is anadvance of very considerable importance.

Initial concentrates of high water content whose ash content as in allflotation processes is influenced by the number of waste particles inextremely fine, highly dispersed form contained therein, can be veryeasily removed from these very fine waste particles, with simultaneousextaction of water, by filtering or centrifuging, so that the very finewaste particles which are not covered with an oil film will very readilypass through the filter apertures and be removed, while, for example,inthe case of through the fabric of the filters or centrifuges. No suchmethod of water removal is possible with normal flotation ofconcentrates, as tests have shown, and it only becomes possible withthis new type of forcing treatment of the material with the flotationreagents.

When used in the dressing of coal, the new process has further markedadvantages, especially with non-coking types of coal. It has been shownthat the coal concentrate obtained, with the particles covered in idealmanner by hydrocarbons, will readily form briquettes, and in someinstances without any further addition of binding material and withouteven being dried. The water in the concentrate has no adverse effects,since it cannot wet the oil-covered particles.

The concentrate can thus be used in mixture with coarser briquettingcoal as a carrier for bonding agents. The low-ash, oil-containingconcentrates of the new process can be used with especial advantage forslowreaction cokes.

A particularly interesting possible use of the new process is theproduction of very pure coal, using only a very small addition of oiland reagents. In consequence, only small quantities of the purercomponents float, which can then be further enriched by repeatedflotation, with perhaps intermediate very fine grinding of theconcentrates.

Reworking of the concentrate arising from the first stage is obviouslypossible, either in flotation cells or with simultaneous forcingtreatment. This is of special importance in producing pure concentratesfrom heavily contaminated coal sludges because the separation of theclay which is deleterious to flotation is rapidly effected, and theconcentrates having little or no clay content can then easily bepurified by further flotation.

We claim:

1. A process for the froth flotation dressing of solid materialscontaining components of varying wettability, which comprises mixingsaid materials with water and a flotation agent to produce a flowablemixture, subjecting the mixture to a forcing treatment by pressingthrough narrow cross-sections such as slits and nozzles to produce anessential unaerated mixture of flotation 'agent wetted components andwater wetted components, and thereafter separating the respectivecomponents by aeration in a froth flotation zone.

2. A process according to claim 1 in which the mixture is subjected tothe forced treatment by being pressed through narrow cross-sections intothe froth flotation zone.

3. A process for the froth flotation dressing of solid materialscontaining components of varying wettability, which comprises mixingsaid materials with water and a flotation agent to produce a flowablepulp, subjecting the pulp to intensive turbulence in a confined zonewhile aerating the pulp therein by admission of air in a finely dividedstate, pressing the aerated pulp from said zone through constrictions toproduce therein flotation agent wetted components and water wettedcomponents, and

thereafter separating the respective components of the aerated pulp inanother treating zone.

4. A process according to claim 3 in which the aerated pulp is passed toa separation zone, and the froth containing the flotation agent wettedcomponents is directly removed from the surface of the pulp.

5. A process according to claim 3 in which the pulp is subjected to theintensive turbulence, aeration and pressing in a baflle plate mill.

6. A process according to claim 3 in which the aerated pulp is passed toa froth flotation zone in which it is subjected to further aeration, andthereafter the froth con- 7 taining the flotation agent wettedcomponents is removed.

7. A process according to claim 1 in which the flotation agent is oil,and defrothed oil-wetted concentrate is filtered from the water and thefines of the water-wetted A component are simultaneously removed.

8. A process according to claim 1 in which the flotation agent is oiland the oil Wetted component is coal, and the separated coal isbriquetted using the adhering oil as a binding agent.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Chemical and Metallurgical Engineering, vol. 26, No. 11, Mar.15, 1922, pages 500503.

Taggart: Handbook of Mineral Dressing, (c) 1945, 10 section 12, page 99.(Copy in Division 55.)

Colliery Engineering, March 1950, pages 109-112. (Copy in ScientificLibrary.)

1. A PROCESS FOR THE FROTH FLOTATION DRESSING OF SOLID MATERIALSCONTAINING COMPONENTS OF VARYING WETTABILITY, WHICH COMPRISES MIXINGSAID MATERIALS WITH WATER AND A FLOTATION AGENT TO PRODUCE A FLOWABLEMIXTURE, SUBJECTING THE MIXTURE TO A FORCING TREATMENT BY PRESSINGTHROUGH NARROW CROSS-SECTIONS SUCH AS SLITS AND NOZZLES TO PRODUCE ANESSENTIAL UNAERATED MIXTURE OF FLOTATION AGENT WETTED COMPONENTS ANDWATER WETTED COMPONENTS, AND THEREAFTER SEPARATING THE RESPECTIVECOMPONENTS BY AERATION IN A FROTH FLOTATION ZONE.